JPH01243257A - Optical pickup - Google Patents

Abstract

PURPOSE:To reduce the constitutive parts and to enable the high speed access in miniaturization and light weight by passing a beam from a semiconductor laser through a diffraction grating, converging upon a recording medium by an objective lens and forming a recording light spot and a reproducing light spot. CONSTITUTION:The beam from the semiconductor laser 102 is converged upon the recording medium 109 formed on the surface of a transparent substrate 114. A reflected beam from the medium 109 is diffracted by the diffraction grating 105, and 1st order diffraction beams 110a and 110b are incident upon photo diodes 111a and 111b. The front faces of these diodes are bonded with polarizing plates 112a and 112b respectively. Then, the beam from the laser 102 is linearly polarized by a polarizing plate 103, and the polarizing direction of its reflected beam is rotated by the direction of recorded magnetization on the medium 109. By this method, a signal recorded on the medium 109 is thus detected out.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to the structure of an optical pickup for recording and reproducing information using light, and in particular to the structure of an optical pickup that uses light to read out recorded signals by rotating the plane of polarization. Regarding the structure of the pickup.

[Prior Art] A conventional optical pickup for magneto-optical recording is composed of a number of optical components such as a polarizing beam splitter and a wave plate for detecting the rotation of polarized light.The basic structure is shown in Fig. 4. Shown below. Figure 4 (a) is a plan view, (b) is (a)
It is a sectional view in which the mirror 405 and the objective lens 406 are particularly taken out.

The light emitted from the semiconductor laser 401 passes through the collimator lens 40
2. Beam shaping prism 403, beam splitter 40
4. The light passes through a mirror 405 and an objective lens 406 and is focused onto an optical disk 407. The reflected light from the optical disk 407 is branched to a detection system by a beam splitter 404, and the light transmitted through the beam splitter 408 passes through a lens 4.09 and is detected by a photodiode 410 to obtain a tracking error signal and a focus error signal. Objective lens 406 is driven by actuator 416 based on these error signals. On the other hand, the light reflected by the beam splitter 408 passes through a half-wave plate 411 and a lens 412, and is split by the polarizing beam splitter 413 depending on the direction of polarization, and is transmitted to the optical disk 407 by the differential output of the two photodiodes 414 and 415. The signal recorded in is detected.

[Problems to be Solved by the Invention] However, in the prior art described above, since there are a large number of optical components, a housing is required to fix each optical component, making the optical pickup large and heavy. The problem is that it cannot be moved at high speed.

The present invention is intended to solve these problems, and its purpose is to provide an optical pickup that is small, lightweight, and capable of high-speed access by reducing the number of components.

[Means for Solving the Problems] The optical pickup of the present invention includes a semiconductor laser, an objective lens that focuses light emitted from the semiconductor laser onto a recording medium,
a diffraction grating in the optical path between the objective lens and the semiconductor laser, a photodiode placed on both sides of the semiconductor laser to detect reflected light from the recording medium, and a photodiode placed in front of the photodiode. The photodiode is divided into a plurality of regions, and the polarizing plate is arranged in front of the photodiode arranged on both sides of the semiconductor laser. It is characterized by the polarization directions being orthogonal.

[Operation] According to the above configuration of the present invention, the light emitted from the semiconductor laser passes through the diffraction grating and is focused on the recording medium by the objective lens, forming a recording optical spot and a reproducing optical spot. .

During reproduction, the reflected light from the recording medium passes through the objective lens again and enters the diffraction grating, and the ±1
The next diffracted light is incident on photodiodes placed on both sides of the semiconductor laser.

The photodiode is divided into multiple areas, and the tracking error signal and focus error signal are detected by the balance of the amount of light incident on each area, and the objective is adjusted so that the light spot is always irradiated on the required position on the recording medium. The position of the lens is controlled.

On the other hand, a method for reading signals recorded on a recording medium will be explained. The polarization plane of the light emitted from the semiconductor laser is rotated by the magnetization of the recording medium, but polarizing plates are placed in front of the photodiodes placed on both sides of the semiconductor laser, so that the polarization directions of each are orthogonal. If the photodiodes are arranged in such a way, the sign of the differential output of the two photodiodes changes depending on which direction the polarization plane of the light returned from the recording medium is rotated, and the direction of magnetization of the recording medium, that is, the signal is detected. be able to.

Hereinafter, the details of the present invention will be shown by examples.

[Embodiment] FIG. 1 is a main configuration diagram of an embodiment of an optical pickup of the present invention, in which (a) is a plan view and (b) is a sectional view. In addition,
The external magnetic field applying means is omitted because it is not essential to the present invention.

A semiconductor laser 102 is attached to a housing 101, and a polarizing plate 103 is bonded to the front surface of the semiconductor laser 102. A diffraction grating 105 is bonded to the semiconductor laser side of the right angle prism 104.

The diffraction grating 105 is made by etching the surface of glass, and the period of the grating is about 4 μm. The diffraction grating 105 is arranged so that the grating grooves are perpendicular to the recording medium 109. Aluminum is vapor-deposited on the slope of the right-angle prism 104 and functions as a mirror 106. The objective lens 107 is attached to the actuator 108 and directs the light emitted from the semiconductor laser 102 to the transparent substrate 114.
The light is focused on a recording medium 109 formed on the surface of the recording medium 109 . The reflected light from the recording medium 109 is diffracted by the diffraction grating 105 and becomes 1
The next diffracted lights 110a and 110b are transmitted to the photodiode 11.
1a and 111b. Photodiode] 11a
, 111b are provided with polarizing plates 112a and 112, respectively.
b is glued.

Next, a method for detecting a focus error signal and a tracking error signal indicating that the light spot is deviated from a desired position on the recording medium will be explained with reference to FIG.

FIG. 2 shows the arrangement of the semiconductor laser 102 and photodiodes 111a and 111b as seen from the diffraction grating side.

The photodiode 111a is divided into four parts, and the photodiode 111b is divided into two parts. Recording medium 10
9 moves away from or approaches the focal position of the objective lens 107, the diffracted light 110a returns onto the photodiode.
, 110b changes as shown in 201 or 202. Therefore, a focus error signal can be obtained by calculating the difference between the diagonal sums of the divided regions in the photodiode 111a.

On the other hand, if the track direction of the recording medium 109 is the direction of the arrow 113 in FIG.
A tracking error signal can be obtained by taking the difference output of the divided regions in step 11b.

Next, a method for detecting the direction of rotation of the polarization plane of reflected light caused by the signal recorded on the recording medium, that is, the direction of magnetization, will be explained using FIG.

FIG. 3(a) shows the semiconductor laser 102,
This is a view of polarizing plates 103, 112a, and 112b bonded to the front surfaces of photodiodes 111a and 111b, respectively. Arrows 301, 302a and 302b in the figure indicate the polarization direction with the highest transmittance in each polarizing plate. Photodiodes 111a, 111b
The polarization direction 302 of the polarizing plates 112a and 112b on the front side of
a.

The polarizing plates 302b are arranged to be perpendicular to each other and to make an angle of 45 degrees with the polarization direction 301 of the polarizing plate 103 in front of the semiconductor laser 102.

The light emitted from the semiconductor laser 102 is polarized by a polarizing plate 103.
The recording medium 109 is irradiated with linearly polarized light that is intensified in the direction of . Signals are recorded in the recording medium 109 in the direction of magnetization, and the polarization direction 3 of the reflected light is determined by the direction of magnetization.
03.304 rotates in either direction as shown in Figure 3(b) and (C). Photodiode 111a, 111
b is divided into a plurality of regions as shown in FIG. When differential output detection is performed by subtraction, if the polarization direction 303 of the reflected light is rotated as shown in FIG. 3(b), this differential output is negative;
When the polarization direction 304 of the reflected light is rotated as shown in FIG. 3(C), it becomes positive, and the direction of magnetization, that is, the signal recorded on the recording medium 109 can be detected.

It should be noted that the present invention can be applied to optical pickups other than the present embodiment in which optical components such as photodiode divisions and diffraction gratings are used. Furthermore, it is also applicable to optical pickups other than those for magneto-optical recording.

[Effects of the Invention] As described above, according to the present invention, the basic components are only a semiconductor laser with a polarizing plate attached, a photodiode with a polarizing plate attached, a diffraction grating, a mirror, and an objective lens. The number of parts can be significantly reduced compared to conventional optical pickups for magneto-optical recording, and the optical pickup can be made smaller and lighter, that is, faster access can be achieved.

Furthermore, since the semiconductor laser and the photodiode are arranged close to each other, there is also the effect that electrical wiring can be concentrated.

The main configuration diagrams include (a) a plan view and (b) a cross-sectional view.

FIG. 2 is a diagram showing the arrangement of a semiconductor laser and a photodiode in an embodiment of the optical pickup of the present invention. Figure 3 (
a) is a diagram showing the arrangement of polarizing plates in an embodiment of the optical pickup of the present invention; FIG. 3(b) is a main configuration diagram of a conventional optical pickup, in which (a) is a plan view and (b) is a sectional view of a part of (a).

101... Housing 102... Semiconductor laser 103... Polarizing plate 104... Right angle prism 105... Diffraction grating 106... Mirror 107... Objective lens 108... Actuator 109... Recording medium 110a, 110b... Diffracted light 111a, 111b... Photodiode 112a
, 112b = polarizing plate 113 ... track direction 114 ... substrate 201 ... light amount distribution 202 ... light amount distribution 301 ... polarization direction 302a, 302b ... polarization direction 303 ... of reflected light Polarization direction 304... Polarization direction of reflected light 401... Semiconductor laser 402... Collimator lens 403... Beam shaping prism 404... Beam splitter 405... Mirror 406... Objective lens 407... - Optical disk 408...Beam splitter 409...Lens 410...Photodiode 411...Half wavelength plate 412...Lens 413...Polarizing beam splitter 414...Photodiode 415...・Photodiode 416 ... Actuator (α) Fig. 1 Fig. 2 (α) (ll)) Color) 1Darkness Wa Introduction 7 (1)ノ

Claims (3)

[Claims] (1) A semiconductor laser, an objective lens that focuses light emitted from the semiconductor laser onto a recording medium, a diffraction grating in the optical path between the objective lens and the semiconductor laser, and a diffraction grating on both sides of the semiconductor laser. An optical pickup comprising: a photodiode arranged to detect reflected light from a recording medium; and a polarizing plate arranged in front of the photodiode. (2) The optical pickup according to item 1, wherein the photodiode is divided into a plurality of regions. (3) The optical pickup according to item 1, wherein the polarization directions of the polarizing plates disposed in front of the photodiodes disposed on both sides of the semiconductor laser are orthogonal to each other.